Allergic diseases affect 30% of the U.S. population. The cytokine interleukin (lL)-4 plays a central role in allergic responses by inducing lgE synthesis and by stimulating several aspects of the inflammatory response. Synthesis of lL-4 is increased in allergic subjects and overexpression of lL-4 in mice leads to the development of "allergic like" inflammatory disease. Production of IL-4 was originally described from T helper (Th) lymphocytes. Indeed, analysis of cytokine profiles was used to define three functional subpopulations of Th cells: ThI, producing lL-2 and interferon v; Th2, producing IL-4 and lL-5; and Th0, having a mixed phenotype. More recently, however, it has been shown that cells other than Th2/Th0 can produce IL-4. For example, human peripheral blood basophils release substantial amounts of lL-4 and other cytokines in response to Crosslinking of membrane-bound lgE. Several studies suggest an important role of lL-4 producing Th cells and basophils in the pathogenesis of allergic inflammation. Delineating the molecular basis of lL-4 gene activation is, therefore, of central importance to our understanding of allergic diseases. The mechanism(s) responsible for mutually exclusive cytokine expression in Th cell subsets are not fully understood. Moreover, no studies have been conducted so far to analyze the transcriptional activation of the lL4 gene in human basophils. The principal investigator has studied in detail two factors having opposite effects on transcriptional activation of the lL-2 and IL-4 genes: nuclear factor (NF)KB and CP2. This project is focused on two specific aims: 1) to understand the mechanisms of ILA gene regulation by these factors and their role in differential gene expression in human Th1 and Th2 clones, and 2) to investigate the mechanisms of lL-4 gene regulation in human basophils, to identify possible transcriptional activators mediating lgE-dependent ILA expression in these cells. DNA-binding assays with proteins extracted from human ragweed antigen (Amb a I)-specific Th1 and Th2 clones and freshly isolated, purified basophils and the analysis of IL4 promoter-driven reporter gene expression in the human T cell leukemia Jurkat will be used to accomplish these aims. Defining the transcriptional factors that regulate the expression of the human ILA gene in Th cells and basophils may, in the long term, lead to novel therapeutic approaches for the treatment of allergic disorders.